The present invention relates to a method of winding a reinforcement layer comprising a fiber cord composed of at least one textile cord on a reinforcement belt wound round a building drum in the production process of a pneumatic radial tire, and more particularly to a method of efficiently forming a reinforcement layer free from a spliced part through continuous winding of a fiber cord round a reinforcement belt provided on a building drum.
In some pneumatic radial tires for a passenger car, a reinforcement layer having a cord angle of substantially 0.degree. relative to the circumferential direction of the tire is wound round at least both edges of at least two reinforcement belts provided on a tread for the purpose of improving high speed durability. FIGS. 6 and 7 are each an example of the tread of a high-performance tire having high speed durability. In FIG. 6, two reinforcement belts B each comprising steel cords are provided on a carcass C of a tread T so that the cord angles cross each other, and both edges of the reinforcement belts B are covered with a reinforcement layer L comprising fiber cords having a cord angle of substantially 0.degree. relative to the circumferential direction of the tire.
When the above-described radial tire travels at a high speed, both edges of the reinforcement belt B are forced up towards the outside in the radial direction by centrifugal force, which causes unfavorable separation. However, the above-described reinforcement layer L serves to inhibit the edges of the reinforcement belt B from being forced up to prevent the occurrence of the separation, which contributes to an improvement in the high speed durability. In order to improve the high speed durability, sometimes the reinforcement layer L is provided so as to cover not only both edges of the reinforcement belt B but also the full width of the reinforcement belt B as shown in FIG. 7.
In the production process of a tire, the winding of the reinforcement layer L round the above-described belt B is conducted on a building drum. As with the reinforcement belt B, the winding of the reinforcement layer L is generally conducted by splicing both ends of a ribbon belt formed by doubling a plurality of fiber cords in parallel. Since the fiber cords of the reinforcement layer are provided in the circumferential direction of the tire, Japanese Patent Laid-Open No. 251203/1987 proposes formation of a reinforcement layer through continuous winding of a single fiber cord coated with rubber in a spiral form in the circumferential direction of the tire without splicing the ribbon belt.
This method of winding a reinforcement layer is excellent in an improvement in the uniformity of a tire because no spliced part is formed. However, in this method, a single fiber cord coated with rubber should be continuously wound several hundred times on a building drum. This takes a very long period of time until the reinforcement layer is formed, which brings about a problem with efficiency. Further, when a reinforcement layer is formed separately on each of the left and right edges of the belt the fiber cord must be cut after winding of one reinforcement layer is completed, and the fiber cord end should be then switched for formation of another reinforcement layer. This takes not only a long time but also much labor.